70 TRANSLOCATION IN PLANTS 



of a loss from the older leaves, but the changes are not 

 statistically significant. The data are presented in Table 

 13. Since these samples were taken during a hot dry 

 period when conditions were favorable for rapid transpira- 

 tion, it was rather surprising to find so little variation 

 in water content. This lack of variation is probably 

 due to the fact that the samples were taken just before 

 direct sunlight struck the leaves in the morning, and shortly 

 after they became shaded in the evening. If samples had 

 been taken at midday and midnight it is probable the water 

 content would have varied more.* Working with bean 

 plants supplied with nitrates at high concentration, Chang 

 (1932) has found diurnal increases in the leaves. His 

 findings are discussed in Sec. 14. 



Even if a diurnal variation were clearly demonstrated, 

 with an increase of nitrogen or ash during the day and a 

 decrease at night, it would not necessarily follow that the 

 increase during the day is brought about by increased 

 transpiration hastening the transport of nitrogen into the 

 leaf. A formation of protein during the day would tend 

 to steepen the diffusion gradient of soluble nitrogen into 

 the leaf, and thus cause a movement bearing no relation 

 to the transpiration stream. The increased protein forma- 

 tion would be expected to result from an increased supply 

 of carbohydrate due to photosynthesis, and need bear 

 no relation to any assumed or real influence of light on 

 protein synthesis. The striking influence of light on the 

 ability of Nitella cells to concentrate halogens in the 

 vacuolar sap, as reported by Hoagland, Hibbard, and 

 Davis (1926), points to light effects entirely independent 

 of transpiration, for these cells were submerged. Brooks 

 (1926) has reported a similar effect of light in causing cells 

 of Valonia, a submerged marine organism, to concentrate 

 dibromophenol indophenol. 



13. Relation of Transpiration to Solute Absorption and 

 Movement in Intact Plants. — As has already been men- 



* I am indebted to Dr. H. L. Chance for making the tedious nitrogen 

 determinations. 



